Electric temperature control system for unpressurized aircraft

ABSTRACT

An electric temperature control system for unpressurized aircraft and methods for operating are disclosed. The electric temperature control system may be electrically powered and used on all-electric aircraft or hybrid aircraft. The electric temperature control system may comprise a vapor cycle cooling system for cooling air and an electric heater for heating air. The electric heater may be a PTC electric heater with individually-controllable heating elements. Various input devices may be disposed in the aircraft allowing an operator to set a compartment temperature, an air source, and a fan speed. A controller controls operations of the electric temperature control system based on feedback received from a plurality of feedback devices and the operator inputs.

CROSS-REFERENCE TO RELATED APPLICATIONS

None.

BACKGROUND OF THE INVENTION 1. Field

The disclosed embodiments relate generally to aircraft temperaturecontrol systems. More specifically, the embodiments relate to electrictemperature control systems for unpressurized aircraft.

2. Description of the Related Art

Various heating and cooling systems for aircraft have been described inthe prior art. U.S. Pat. No. 6,526,775 to Asfia et al. describes anelectronic air conditioning system for pressurized aircraft. U.S. Pat.No. 7,207,521 to Atkey et al. describes an electric-based secondarypower system for pressurized aircraft. U.S. Pat. No. 8,973,393 to Atkeyet al. describes an electrical cooling system for use in groundoperations of an aircraft. U.S. Pat. No. 9,617,005 to Schiff describes amethod for replacing an engine-powered air conditioning unit with anelectric air conditioning unit.

SUMMARY

Disclosed embodiments are generally directed towards an electrictemperature control system for providing heating and cooling inunpressurized aircraft. The electric temperature control system maycomprise a vapor cycle cooling system for cooling air and an electricheater for heating air. User input controls may be provided allowing auser to set a desired temperature, fan speed, and air source. The userinputs, along with various feedback mechanisms, may dictate theoperations of the temperature control system to achieve the desiredtemperature in the aircraft.

In some aspects, the techniques described herein relate to an electrictemperature control system for unpressurized aircraft, including: anelectrical power source for powering the electric temperature controlsystem; a vapor cycle cooling system for cooling air; an electric heaterfor heating air; a source selection valve for selecting an air source;at least one air inlet fluidly connected to the source selection valve;an input device for receiving a user input of a target temperature valuein a compartment of the unpressurized aircraft; a plurality oftemperature sensors; and one or more non-transitory computer-readablemedia storing computer-executable instructions that, when executed by atleast one processor, carry out actions including: receiving, from atemperature sensor of the plurality of temperature sensors, acompartment temperature value; receiving, from the input device, thetarget temperature value; determining, based on a difference between thecompartment temperature value and the target temperature value, whetherheating or cooling is required; responsive to determining that heatingis required, enabling the electric heater; and responsive to determiningthat cooling is required, enabling the vapor cycle cooling system.

In some aspects, the techniques described herein relate to a method forconditioning an unpressurized aircraft using an electric temperaturecontrol system, the method including: receiving, from an operator andvia an input device, a target temperature value of a compartment of theunpressurized aircraft; receiving, from a temperature sensor, acompartment temperature value of air in the compartment; determining,based on a difference between the compartment temperature value and thetarget temperature value, whether heating or cooling of the compartmentis required; responsive to determining that cooling is required:enabling a vapor cycle cooling system, the vapor cycle cooling systemincluding a compressor, a condenser heat exchanger, a condenser blower,and an evaporator heat exchanger; modulating a cooling capacity of thecondenser heat exchanger and the condenser blower based on thedifference between the compartment temperature value and the targettemperature value; and cycling refrigerant through the vapor cyclecooling system for cooling of air directed over the evaporator heatexchanger; and responsive to determining that heating is required:enabling an electric heater; determining an amount of heating to provideto the compartment based on the difference between the compartmenttemperature value and the target temperature value; setting a heatingcapacity of the electric heater based on the difference; and directing,via a blower, the air past the electric heater for heating and into thecompartment.

In some aspects, the techniques described herein relate to an electrictemperature control system for unpressurized aircraft, including: anelectrical power source for powering the electric temperature controlsystem; a vapor cycle cooling system for providing cooling to acompartment of the unpressurized aircraft; an electric heater forproviding heating to the compartment of the unpressurized aircraft; anambient air inlet fluidly connected to a source selection valve; arecirculation air inlet fluidly connected to the source selection valve;a blower configured to direct air to the vapor cycle cooling system andthe electric heater and further to the compartment; the source selectionvalve, wherein the source selection valve is actuatable to provide oneof ambient air from the ambient air inlet or recirculation air from therecirculation air inlet to the blower; an input device for selecting atarget temperature value for the compartment; and at least onecontroller configured to carry out actions including: determining, basedon a difference between the target temperature value and a compartmenttemperature value, whether heating or cooling of the compartment isrequired; and responsive to determining whether heating or cooling ofthe compartment is required, adjusting a position of the sourceselection valve.

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the detaileddescription. This summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter. Other aspectsand advantages of the invention will be apparent from the followingdetailed description of the embodiments and the accompanying drawingfigures.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Illustrative embodiments are described in detail below with reference tothe attached drawing figures, which are incorporated by reference hereinand wherein:

FIG. 1 illustrates an aircraft for some embodiments;

FIG. 2 illustrates heating and cooling components of an electrictemperature control system for some embodiments;

FIG. 3 illustrates the electric temperature control system for someembodiments;

FIG. 4 illustrates a control architecture for the electric temperaturecontrol system for some embodiments;

FIG. 5A illustrates operations of the electric temperature controlsystem for some embodiments;

FIG. 5B illustrates cooling operations of the electric temperaturecontrol system for some embodiments; and

FIG. 5C illustrates heating operations of the electric temperaturecontrol system for some embodiments.

The drawing figures do not limit the invention to the specificembodiments disclosed and described herein. The drawings are notnecessarily to scale, emphasis instead being placed upon clearlyillustrating the principles of the invention.

DETAILED DESCRIPTION

The following detailed description references the accompanying drawingsthat illustrate specific embodiments in which the invention can bepracticed. The embodiments are intended to describe aspects of theinvention in sufficient detail to enable those skilled in the art topractice the invention. Other embodiments can be utilized, and changescan be made without departing from the scope of the invention. Thefollowing detailed description is, therefore, not to be taken in alimiting sense. The scope of the invention is defined only by theappended claims, along with the full scope of equivalents to which suchclaims are entitled.

In this description, references to “one embodiment,” “an embodiment,” or“embodiments” mean that the feature or features being referred to areincluded in at least one embodiment of the technology. Separatereferences to “one embodiment,” “an embodiment,” or “embodiments” inthis description do not necessarily refer to the same embodiment and arealso not mutually exclusive unless so stated and/or except as will bereadily apparent to those skilled in the art from the description. Forexample, a feature, structure, act, etc. described in one embodiment mayalso be included in other embodiments but is not necessarily included.Thus, the technology can include a variety of combinations and/orintegrations of the embodiments described herein.

Traditional, turbine engine aircraft extract bleed air from the engineto power temperature control systems that provide heating and cooling tothe aircraft. For electric and hybrid aircraft, little to no enginebleed air is available for powering temperature control systems. Thus,electric and hybrid aircraft must rely substantially or completely onelectric power.

What is needed are improved temperature control systems for aircraftthat do not rely upon engine bleed air. Further, what is needed aretemperature control systems that are substantially or entirelyelectrically powered. Further still, what is needed are temperaturecontrol systems with improved control to improve the efficiency thereof.

Embodiments disclosed herein are generally related to an electrictemperature control system for unpressurized aircraft. The electrictemperature control system may comprise a vapor cycle cooling system forcooling air and an electric heater for heating air. The temperaturecontrol system may be powered by an electrical power source. Theelectric heater may be a positive thermal coefficient (PTC) heatercomprising a plurality of individually-controllable heating elementsthat may be modulated to reach a desired temperature in the aircraft. Anoperator, such as a flight crew member, may provide inputs to thetemperature control system. The operator may set a desired temperature,a desired fan speed, and a desired air source. Based on the user inputsand various feedback devices, the temperature control system maydetermine whether heating or cooling is required, which air source touse, and various other operating parameters of the electric temperaturecontrol system, as discussed in detail below. A plurality of temperaturesensors may be disposed throughout the temperature control system toprovide feedback to the control system.

FIG. 1 illustrates an aircraft 100 with a cabin 102 and a cockpit 104,which collectively may represent an occupied compartment 106. Theoccupied compartment 106 may be occupied by one or more of passengers orcargo. Aircraft 100 may be an unpressurized aircraft such that occupiedcompartment 106 is also unpressurized. Unpressurized aircraft requirethat the cabin be ventilated, and temperature controlled to maintain acomfortable environment for the passengers, crew, ortemperature-sensitive cargo. Unpressurized aircraft are typicallyoperated up to altitudes of about 10,000-feet above sea level such thatsufficient oxygen is available for crew and passengers without providingpressurization. Aircraft 100 may be a conventional turbine engineaircraft, a hybrid aircraft comprising both a turbine engine and anelectric motor, or a fully-electric aircraft.

FIG. 2 illustrates various components of a temperature control system200 for some embodiments of the invention. The dash-dotted linesrepresent fluid connections between the components, and the solid linesrepresent pneumatic connections between components. The working fluidmay be a refrigerant, such as R-134a, R-32, or any other refrigerant nowknown or later developed.

Air inlet sources for temperature control system 200 may include cabinair static inlet 202, condenser ram air inlet 204, and recirculation airinlet 206.

Cabin air static inlet 202 may be located in aircraft 100 in a locationthat substantially eliminates any ingestion of engine exhaust, runwayfluids, or other contaminants. Cabin air static inlet 202 may be sizedappropriately based on the ventilation and cooling requirements ofaircraft 100. Cabin air static inlet 202 may pull air from a pressureneutral portion of the fuselage of aircraft 100.

Condenser ram air inlet 204 may similarly be located within aircraft 100to substantially eliminate the ingestion of engine exhaust, runwayfluids, or any other contaminants. Condenser ram air inlet 204 may besized appropriately based on the heat rejection requirement of acondenser heat exchanger (HX) 210, discussed further below.

Recirculation air inlet 206 may be located in cabin 102. For aircraftwith multiple independent temperature control zones (discussed furtherbelow), each zone may have a recirculation air inlet 206. For example,if cabin 102 and cockpit 104 are separately controlled temperaturezones, a recirculation air inlet 206 may be located in each of cabin 102and cockpit 104. Recirculation air inlet 206 may comprise a filter toreduce dust and other contaminants from the cabin air. The size ofrecirculation air inlet 206 may depend on the ventilation and coolingrequirements of aircraft 100.

Temperature control system 200 may comprise a vapor cooling cycle systemcomprising a compressor 208, a condenser HX 210, a condenser blower 212,a receiver drier 214, and an evaporator HX 216. The vapor cooling cyclesystem may cool air that is provided to occupied compartment 106, asdiscussed further below. An electric heater 218 may heat air that isprovided to occupied compartment 106, also discussed further below.Temperature control system 200 may further comprise a source selectionvalve 220 for toggling a source of air provided to electric heater 218and the vapor cycle cooling system between cabin air static inlet 202and recirculation air inlet 206. Add-heat valves 222 may modulate theamount of heating and cooling air directed to lower outlets 223 (e.g., afloor area) of occupied compartment 106. A supply blower 224 may blowair over evaporator HX 216 or add-heat valves 222 depending on the modeof operation of temperature control system 200. Air from add-heat valves222 may then be directed towards electric heater 218 for heatingthereof.

Various temperature sensors may be distributed throughout temperaturecontrol system 200. A supply temperature sensor 226 may measure the airtemperature exiting supply blower 224. A heat supply temperature sensor228 may measure the air temperature exiting electric heater 218. A coldsupply temperature sensor 230 may measure the air temperature exitingevaporator HX 216. A compartment temperature sensor 232 may measure theair temperature in occupied compartment 106. An ambient temperaturesensor 234 (see FIG. 3 ) may measure ambient air temperature.Temperature sensors 226, 228, 230, 232, 234 may be resistive thermaldevice (RTD) sensors. In some embodiments, temperature sensors 226, 228,230, 232, 234 may be thermocouples or thermistors.

In some embodiments, a heater overtemperature switch 236 is coupled toelectric heater 218 and configured to detect overheating of electricheater 218. If a thermal runaway event is detected, heaterovertemperature switch 236 may automatically cut power to electricheater 218. Heater overtemperature switch 236 may comprise two electriccontacts that are closed when electric heater 218 operates in a safetemperature range and open when a thermal runaway event is sensed.

Temperature control system 200 may be controlled by a controller 402(see FIG. 4 ). Each temperature sensor 226, 228, 230, 232, 234 andheater overtemperature switch 236 may be communicatively coupled tocontroller 402. Based at least in part on the data from temperaturesensors 226, 228, 230, 232, 234, controller 402 may determine whetherheating or cooling is required and control the operations of thecomponents in temperature control system 200, as discussed in furtherdetail below.

When cooling is required, the components of the vapor cycle coolingsystem may be enabled. Compressor 208 may be configured to compressrefrigerant into a high-pressure gas. Compressor 208 may be a positivedisplacement compressor with variable displacement, such as a variablespeed scroll or a variable stroke piston compressor. Further, asdiscussed below, compressor 208 may be modulated based on the coolingrequired in occupied compartment 106. Compressor 208 may be driven by anelectric motor. By utilizing a variable displacement compressor, thepower draw thereof may be limited based on the available aircraftelectrical power.

After the refrigerant is compressed by compressor 208, the refrigerantis passed to condenser HX 210. Condenser blower 212 may blow air fromcondenser ram air inlet 204 across condenser HX 210. As the ambient airpasses over condenser HX 210, heat is extracted from the refrigerant,thereby condensing the refrigerant into a high-pressure liquid. In someembodiments, condenser HX 210 is a dual path parallel flow HX and may bedriven by an electric motor. Condenser blower 212 may be electricallypowered and may be an axial or a centrifugal blower. After therecirculated air is passed over condenser HX 210, the air may bedirected overboard. Condenser blower 212 may draw ambient air duringboth in-flight and ground operations of temperature control system 200.Condenser ram air inlet 204 may be fluidly connected to condenser blower212.

From condenser HX 210, the refrigerant is provided to evaporator HX 216.As refrigerant flows from condenser HX 210 to evaporator HX 216,receiver drier 214 may passively remove moisture from the refrigerant.Receiver drier 214 may comprise a container having an inlet tube inwhich refrigerant from condenser HX 210 may be discharged. A desiccantbag in the container allows moisture in the refrigerant to be captured.Receiver drier 214 may also comprise an outlet tube at a lower point inthe container that provides the liquid refrigerant to evaporator HX 216.At evaporator HX 216, the refrigerant may be expanded into alow-pressure and low-temperature gas. In some embodiments, evaporator HX216 is a dual path parallel flow HX. Evaporator HX 216 may comprise anexpansion valve through which the liquid refrigerant flows andevaporates into a cold gas.

Coupled to evaporator HX 216 is supply blower 224 which blows air overevaporator HX 216 that is then cooled by evaporator HX 216 as thegaseous cold refrigerant circulates through HX channel. The cooled airmay then be directed to occupied compartment 106.

When heating of occupied compartment 106 is required, the vapor cyclecooling components (i.e., compressor 208, condenser HX 210, condenserblower 212, drier 214, and evaporator HX 216) may be disabled. Electricheater 218 may then be enabled. In some embodiments, electric heater 218comprises a PTC electric heater. In other embodiments, electric heater218 is a resistive type electric heater.

Electric heater 218 may comprise a plurality of individuallycontrollable heating elements. As discussed further below, based on theamount of heating required to reach the target temperature value inoccupied compartment 106, a heating element in electric heater 218 maybe pulse width modulated until the heating element reaches a maximumheating capacity. After reaching the maximum heating capacity, the nextheating element may be turned on and modulated to fine tune thetemperature provided to occupied compartment 106 to the desiredtemperature value.

Heating elements constructed from PTC materials (e.g., ceramic stones)may be designed to self-regulate their maximum temperature based oninnate compositional characteristics of the ceramic core of the heatingmodule. When a PTC ceramic heater element is utilized in athermostatically controlled system, intermediate heating temperaturesbetween the ambient air and the self-regulation temperature of the PTCheater element may be achieved by switching the PTC heater elements onand off in response to temperature sensor readings. Using a PTC heateras the heating element may guarantee that even if a defectivethermostatic switching mechanism became stuck in an on-state, the designtemperature of the PTC module cannot be exceeded as the heating elementproduces substantially little heating power when heated above the designtemperature. The design temperature may be configured such that smokeand fire hazards seen in common heaters are substantially eliminated.

FIG. 3 illustrates temperature control system 200 including the controlelements and input elements thereof for some embodiments. Thedash-dotted lines represent refrigerant connections between thecomponents, the solid lines represent pneumatic connections betweencomponents, and the dashed lines represent electrical signalstransmitted between components.

Temperature control system 200 may comprise a set of inputs 302 allowingan operator to input desired operational parameters. Inputs 302 maycomprise an air source input 304, an air conditioning input 306, atemperature input 308, a fan speed input 310, or any combinationthereof. Air source input 304 may allow the operator to choose betweenrecirculating air, ambient air, or a normalized mode, wherein controller402 may determine whether to provide recirculating air or ambient airfor the air inlet. Air source input 304 may comprise a three-positiontoggle switch, a touch screen interface, a series of buttons, or anyother user interface arrangement.

Air conditioning input 306 may allow the operator to turn temperaturecontrol system 200 on and off. When temperature control system 200 ison, temperature control system 200 may operate in a normalized mode,wherein controller 402 determines whether heating or cooling of occupiedcompartment 106 is required. During operations of aircraft 100,temperature control system 200 may be always on, and turning temperaturecontrol system 200 off may be used in case of an emergency, such asoverheating of electric heater 218 or low battery of the electric powersource powering temperature control system 200. Air conditioning input306 may be a two-position toggle switch, a pair of button switches, atouch screen interface, or any other user interface arrangement.

Temperature input 308 may comprise an input for setting the targettemperature in occupied compartment 106. Temperature input 308 may be alinearly variable input. In some embodiments, temperature input 308comprises a rotary knob with a “full cold” setting near an 8-o'clockposition and a “full hot” setting near a 4-o'clock position. Other userinput arrangements for temperature input 308, such as a variable linearinput, or a variable touch screen selection, a slider element, or anyother linearly variable input element, are within the scope hereof. Thefull cold setting may set the target temperature to be near 65 degreesFahrenheit, and the full hot setting may set the target temperature tobe near 85 degrees Fahrenheit. If occupied compartment 106 is fortransporting goods (e.g., food, packages, etc.) the full coldtemperature value and the full hot temperature value may be suitablyadjusted. A “maximum cold” setting may be provided for cooling occupiedcompartment 106. In some embodiments, temperature input 308 may beinserted into a potentiometer having a detent for the maximum coldsetting. When controller 402 detects temperature input 308 in themaximum cold setting, add-heat valves 222 may be toggled to providecooled air to both the lower outlet 223 and the upper outlet 225 ofoccupied compartment 106.

Fan speed input 310 may comprise an input for setting the fan speed ofsupply blower 224. In some embodiments, fan speed input 310 comprises arotary knob with a “slow” setting near an 8-o'clock position and a“fast” setting near a 4-o'clock position. In some embodiments, fan speedinput 310 comprises a touch screen interface, a slider element, or anyother linearly variable input element. Fan speed input 310 may comprisea detent for turning off supply blower 224. In some embodiments, fanspeed input 310 may be inserted into a potentiometer having a detent forthe off setting. In some embodiments, when supply blower 224 is turnedoff, temperature control system 200 is shut down. For aircraft 100 withmultiple supply blowers 224, a fan speed input 310 may be provided foreach supply blower 224.

In some embodiments, inputs 302 are located in cabin 102, cockpit 104,or any other location in aircraft 100. In some embodiments, inputs 302are physical input devices as described above. Alternatively, inputs 302may be provided via a touch screen interface. In some embodiments,temperature control system 200 may be controlled remotely and inputs 302may be disposed in a remote location. For example, it is contemplatedthat inputs 302 may be controlled from a mobile device (e.g., via aBLUETOOTH® connection), such that a flight crew member can controltemperature control system 200 while outside of aircraft 100, such aswhen aircraft 100 is taxied on a runway.

Each input 302 may be communicatively coupled to controller 402. Basedon the setting of inputs 302, controller 402 may adjust the operationsof temperature control system 200 as detailed below with respect to FIG.4 .

Looking first at air source input 304, when controller 402 detects airsource input 304 set to the recirculating mode, controller 402 mayposition source selection valve 220 to allow air from recirculation airinlet 206 to be passed to supply blower 224. When controller 402 detectsair source input 304 set to the fresh air mode, controller 402 mayposition source selection valve 220 to allow air from cabin air staticinlet 202 to pass to supply blower 224. Cabin air static inlet 202 maybe fluidly connected to supply blower 224. As described above, when airsource input 304 is in the normalized mode, controller 402 determineswhether source selection valve 220 should provide recirculating air fromrecirculation air inlet 206 or fresh air from cabin air static inlet202. The determination may be made based on the ambient air temperatureas detected by ambient temperature sensor 234. In some embodiments, ifthe ambient air temperature is below a maximum cooling temperaturecapable of being provided by the vapor cycle cooling system, controller402 positions source selection valve 220 to receive ambient air fromcabin air static inlet 202. If the ambient air temperature is above themaximum cooling temperature capable of being provided by the vapor cyclecooling system, controller 402 may position source selection valve 220to receive recirculated air from recirculation air inlet 206. Controller402 may constantly or nearly constantly monitor temperature readingsfrom ambient temperature sensor 234 and compare the readings to themaximum cooling temperature value for determining whether to providesupply blower 224 with fresh air or recirculated air. Source selectionvalve 220 may be a single valve with multiple inputs and a single outputor a pair of valves for each inlet that work in concert to control thesource of air.

The input to air conditioning input 306 may turn temperature controlsystem 200 on and off. When temperature control system 200 is on andcontroller 402 determines that cooling is required, controller 402 maycommand compressor 208 to turn on and electric heater 218 to turn off.As described above, compressor 208 compresses refrigerant, passes therefrigerant to condenser HX 210 to be condensed, and thereafterevaporator HX 216 expands and cools the refrigerant such that airdirected over evaporator HX 216 by supply blower 224 is cooled beforeentering occupied compartment 106. Based on the required cooling,controller 402 may modulate the cooling capacity of compressor 208. Insome embodiments, the cooling capacity is determined based on amagnitude of error between the target temperature (as set by temperatureinput 308) and the actual temperature of occupied compartment 106 (asdetected by compartment temperature sensor 232). Thus, when asubstantially large difference between the target temperature and thecompartment temperature is present, controller 402 may modulate thecompressor 208 to operate at a substantially high cooling capacity. Asoccupied compartment 106 is cooled and the temperature differencedecreases, controller 402 may decrease the cooling capacity ofcompressor 208. As described above, during cooling, if temperature input308 is set to the max cold position, controller 402 may positionadd-heat valves 222 to also provide cooled air to lower outlets 223 ofoccupied compartment 106. In some embodiments, cold air is continuouslyprovided to upper outlets 225 (e.g., an overhead area) of occupiedcompartment 106. When temperature control system 200 provides heating,the heated air may be directed out of lower outlets 223.

When controller 402 determines that heating is required, controller 402may disable the vapor cycle cooling system and enable electric heater218. Controller 402 may compare the difference between the targettemperature and the temperature in occupied compartment 106 to determinehow many heating elements should be turned fully on. The next availableheating element may then be pulse width modulated by controller 402 toheat the air to the target temperature value. In some embodiments, ifthe target temperature value is above a threshold temperature value,controller 402 positions source selection valve 220 to providerecirculation air from recirculation air inlet 206 to source selectionvalve 220. In some embodiments, the threshold temperature value is amiddle temperature value between the full cold and the hot cold settings(e.g., 75° F.).

FIG. 4 shows an exemplary control architecture 400 for temperaturecontrol system 200 for some embodiments. Control architecture 400 maycomprise controller 402 communicatively coupled to various components oftemperature control system 200. In some embodiments, controller 402receives input from temperature sensors 226, 228, 230, 232, 234, heaterovertemperature switch 236, aircraft status 404, electric power source406, inputs 302, or any combination thereof. Based on the receivedinputs, controller 402 may output commands to compressor 208, electricheater 218, source selection valve 220, add-heat valves 222, supplyblower 224, or any combination thereof. While unidirectionalcommunication links are illustrated in FIG. 4 , it should be noted thatcontroller 402 may be bidirectionally coupled to any of the componentsin temperature control system 200. Further, controller 402 may beconnected to other components of temperature control system 200 notdepicted in FIG. 4 for turning said components on and off as necessary.For example, controller 402 may signal the motor powering compressor 208on and off.

Controller 402 may be a microcontroller, a microprocessor, orprogrammable logic controller (PLC). Controller 402 could also be acomputer (e.g., the aircraft flight control computer or a separatecomputer), having a memory 408, including a non-transitorycomputer-readable medium for storing software 410, and a processor 412for executing instructions of software 410. In certain embodiments,some, or all of software 410 is configured as firmware for providinglow-level control of devices of the temperature control system 200.Communication between controller 402 and devices of temperature controlsystem 200 may be by at least one of a wired and/or wirelesscommunication media.

Controller 402 may receive aircraft information via the aircraft status404. Aircraft status 404 may indicate various operating parameters ofaircraft 100. For example, aircraft status 404 may indicate electricalpower generation status and whether aircraft 100 is grounded, taxiing,in takeoff, cruising, or landing. The operator may direct the controller402 via inputs 302 to adjust the air temperature of the occupiedcompartment 106. Controller 402 may then adjust the operations of one ormore of compressor 208, electric heater 218, source selection valve 220,add-heat valves 222, or supply blower 224 to achieve the target airtemperature within the occupied compartment 106. Controller 402 mayalter the configuration of the valves 220, 222 by various mechanisms.For example, controller 402 may set a valve position that is maintaineduntil a new valve position is instructed by controller 402. In anotherexample, controller 402 may enact a duty cycle in which the valve ismodulated towards an open or a closed direction for a specified amountof time over a certain time period. For example, add-heat valves 222 maybe actuated between a fully-closed position (e.g., zero degrees) and afully-open position (e.g., 90 degrees). For instance, a valve may bemoved in the open direction for two seconds and held in place for onesecond, which may repeat for a predetermined period of time (e.g., oneminute). In some embodiments, valves 220, 222 are one of a ball, abutterfly, or a gate-type valve. In some embodiments, valves 220, 222are configured with valve sensors from which controller 402 may deriveinformation such as an instantaneous position or rate of response of thevalve 220, 222. Valves 220, 222 may be controlled pneumatically orelectrically. The valve sensors may be at least one of a potentiometer,a resolver, or a RVDT (rotary variable differential transformer).

Controller 402 may execute control algorithms that may include afeedback mechanism which depends on a difference or error term betweenthe target zone temperature and the current temperature of occupiedcompartment 106 as sensed by compartment temperature sensor 232. In someembodiment, the controller 402 comprises aproportional-integral-derivative (PID) control algorithm in which theproportional term adjusts the position of the valves in proportion tothe magnitude of the error term, the integral term adjusts the positionof the valves in proportion to both the magnitude and the duration ofthe error term by integrating over time to account for any cumulativeerror, and the derivative term adjusts the position of the valves inproportion to the rate of change of the error term over time. The termsare weighted based on gains (e.g., coefficients), which may be tuned toprovide a stable valve position with a minimal error term. In someembodiments, the controller 402 is a proportional-integral (PI)controller in which the derivative term is not used (e.g., set to zero).In some embodiments, the controller 402 is a proportional (P) controllerin which the derivative term and the integral term are not used. In someembodiments, the valve position feedback may be used as a surrogate forrate feedback (e.g., derivative controller action).

The controller 402 reduces the error term based on feedback from thetemperature sensors 226, 228, 230, 232, 234, as well as the valvesensors, which may be used to improve performance of the temperaturecontrol system 200 in addition to avoiding unsafe deflection of thevalves 220, 222.

As previously described, temperature control system 200 may beelectrically-powered by one or more electric power sources 406. Electricpower source 406 may also be communicatively coupled to controller 402such that controller 402 may monitor the performance thereof. In someembodiments, electric power source 406 is supplied AC or DC voltage froma power bus of aircraft 100. The power bus, in turn, may be fed from abattery pack, an engine mounted generator, or the like. Whileembodiments are described herein with reference to anelectrically-powered temperature control system 200, it should be notedthat temperature control system 200 may be used on a turbine aircraftand extract bleed air as a power source. Controller 402 may monitorelectric power source 406 for power failures, excessive current draws,and other like aberrational performance issues. As one example, anexcessive current draw may cause controller 402 to shut off airconditioning input 306, and thereby, temperature control system 200, toreduce the load on electric power source 406. When operating on theground, temperature control system 200 may be powered by a ground powerunit that can electrically power temperature control system 200.On-ground operations may be an aircraft status 404 input to controller402.

In some embodiments, controller 402 is configured to adjust theoperations of temperature control system 200 based at least in part onthe capacity of electric power source 406. For example, compressor 208and/or electric heater 218 may be limited based to preserve batterypower. Similarly, controller 402 may throttle temperature control system200 based on aircraft status 404, such as when aircraft status 404indicates 100 is in-flight.

FIG. 5A, FIG. 5B, and FIG. 5C collectively illustrate a method 500 foroperations of temperature control system 200 for some embodiments.Temperature control system 200 may be controlled by controller 402 basedon various inputs 302 as illustrated with respect to FIG. 4 above. FIG.5A depicts initial operations of temperature control system 200 for someembodiments. Operations of temperature control system 200 may begin atstart 502.

At test 504, it may be determined whether supply blower 224 has beenturned on. As described above, supply blower 224 may be turned on by theoperator via fan speed input 310. If supply blower 224 is off,processing may proceed to step 506. If supply blower 224 is on,processing may proceed to step 510.

When supply blower 224 is off, at step 506, controller 402 may commandtemperature control system 200 off. Thereafter, at step 508, sourceselection valve 220 may be positioned to provide ambient air to occupiedcompartment 106 from cabin air static inlet 202. Processing may thenloop back to test 504 such that controller 402 is substantiallyconstantly monitoring the setting of fan speed input 310 to determinewhether temperature control system 200 should be on or off.

When supply blower 224 is on as determined at test 504, at step 510,controller 402 may position source selection valve 220 to providerecirculation air from recirculation air inlet 206 to occupiedcompartment 106, supply blower 224 may be set to the input speedreceived from fan speed input 310, and controller 402 may ensure thatelectric heater 218 and the vapor cycle cooling system components areturned off.

Next, at test 512, controller 402 may determine whether the temperatureof occupied compartment 106 is greater or less than the target zonetemperature of occupied compartment 106 as obtained from temperatureinput 308. If the temperature of occupied compartment 106 is greaterthan the target zone temperature, processing may proceed to node A (seeFIG. 5B) for cooling of occupied compartment 106. If the temperature ofoccupied compartment 106 is less than the target zone temperature,processing may proceed to node B (see FIG. 5C) for heating of occupiedcompartment 106. In some embodiments, temperature control system 200 isoperated with a hysteresis band to prevent oscillations between theheating and cooling operations. The hysteresis band may be ±5° F., forexample. In some embodiments, the hysteresis band is configurable by theoperator.

Turning now to FIG. 5B, cooling operations of temperature control system200 are illustrated for some embodiments. Processing may begin from nodeA as illustrated in 5A.

At step 514, controller 402 may ensure that electric heater 218 isturned off and command the vapor cycle cooling system on. Thereafter, attest 516, it may be determined whether temperature input 308 is set tothe max cold position described above. If temperature input 308 is setto the max cold position, processing may proceed to step 518. Iftemperature input 308 is not set to max cold, processing may proceed tosteps 520 and 528. It should be noted that controller 402 may constantlymonitor the input from temperature input 308 to determine whether themax cold setting is active.

At step 518, for operating in the max cooling mode, controller 402 mayactuate add-heat valves 222 to direct cooled air to the lower outlet 223(in addition to upper outlet 225) and command compressor 208 andcondenser blower 212 to operate at a maximum capacity. Thus, the maximumcooling potential of temperature control system 200 may be realized.

At test 516, when temperature control system 200 is not providingcooling in the maximum cooling mode, processing may proceed in parallelbeginning with step 520 and step 528.

Looking first at step 520, controller 402 may continuously monitor thedifference between the external ambient temperature (as received fromambient temperature sensor 234) and the recirculation air temperature(as received from compartment temperature sensor 232). At test 522, itmay be determined whether the ambient temperature is below therecirculation temperature and whether the target zone temperature is inthe bottom half of the temperature range (e.g., below 75° F. for atemperature range of 65° F. to 85° F.). If the ambient temperature isless than the recirculation temperature and the target zone temperatureis in the bottom half of the temperature range, at step 524, sourceselection valve 220 may be positioned to provide ambient air to supplyblower 224, thus providing supply blower 224 with the coolest air sourceavailable. If the ambient temperature is not less than the recirculationtemperature or the target zone temperature is not in the bottom half ofthe temperature range, at step 526, source selection valve 220 may bepositioned to provide recirculation air to supply blower 224. It shouldbe noted that setting air source input 304 to either the recirculationor fresh air setting may override the processing of steps 520-526 andcontroller 402 may actuate source selection valve 220 to provide airfrom the set position of air source input 304.

Looking now at step 528, controller 402 may continuously monitor thedifference between the temperature of occupied compartment 106 (asreceived from compartment temperature sensor 232) and the target zonetemperature (as received from temperature input 308). Based on thedifference, at step 530, controller 402 may modulate the cooling rate ofcompressor 208 and condenser blower 212. As the difference increases,controller 402 may increase the cooling rate of compressor 208 andcondenser blower 212 such that the vapor cycle cooling system cools airat a higher rate. As the difference decreases and occupied compartment106 is cooled, compressor 208 and condenser blower 212 may be throttleddown to reduce power consumption. As described above, steps 520-526 andsteps 528-530 may happen substantially in parallel and may continuouslyloop while temperature control system 200 is cooling occupiedcompartment 106.

Turning now to FIG. 5C, heating operations of temperature control system200 are illustrated for some embodiments. Processing may begin from nodeB.

At step 532, controller 402 may ensure that the vapor cycle coolingsystem is turned off and turn on electric heater 218. From step 532,processing may proceed substantially in parallel at test 534 and step540.

Looking first at test 534, it may be determined whether the target zonetemperature is on the upper half of the temperature range of temperaturecontrol system 200 (e.g., above 75° F. for a temperature range of 65° F.to 85° F.). If no, at step 536, source selection valve 220 may bepositioned to provide ambient air from cabin air static inlet 202 tosupply blower 224. If yes, at step 538, source selection valve 220 maybe positioned to provide recirculation air from recirculation air inlet206 to supply blower 224.

At step 540, controller 402 may determine the difference between thetarget temperature and the temperature of occupied compartment 106 asprovided by compartment temperature sensor 232. At step 542, thetemperature difference between the target temperature and thecompartment temperature may be utilized to determine a target ducttemperature which, in turn, may be compared against a measured ducttemperature. The measured duct temperature may be obtained from heatsupply temperature sensor 228. The difference between the target ducttemperature and the measured duct temperature results in a ducttemperature error. Based on the duct temperature error, at step 544,controller 402 may turn on a number of heating elements of electricheater 218 to a fully-on state. An additional heating element may bepulse width modulated by 238 to fine tune the output temperature ofelectric heater 218. It should be noted that electric heater 218 may beoperated with no heating elements in the fully-on state and only have amodulating heating element if the duct temperature error is sufficientlylow. In some embodiments, a predetermined or threshold duct temperatureerror may be set that automatically turns a preset number of heatingelements to the fully-on state. For example, if electric heater 218 is afour-element heater, for a duct temperature error above 40° F.,controller 402 may automatically set two elements to operate at maximumcapacity, PWM a third element, and leave the remaining elements off tofine tune the outlet temperature.

Next, at test 546, it may be determined whether the modulated heatingelement has reached 100% capacity (i.e., fully-on). If no, processingloops back to test 546 and controller 402 monitors the capacity of themodulated heating element. If yes, at step 548, with the modulatedheating element at 100%, controller 402 may enable and begin modulatingthe next heating element of electric heater 218. Processing may thenproceed back to test 546.

Typically, PTC electric heaters are operated with all the elementsmodulating simultaneously. Operating the heater in this way requireshigh current and reduces the efficiency of controller 402, batteries,and other components in temperature control system 200. By individuallycontrolling the heating elements of electric heater 218 and operatingonly the required elements at full capacity before modulating on anadditional heating element to fine tune the output temperature, a moreefficient temperature control system 200 may be realized.

In some embodiments, temperature control system 200 is configured tooperate in an economy mode to reduce the power consumption of electricpower source 406. The economy mode may limit the power draw ofcompressor 208 and electric heater 218. Other components, such as supplyblower 224, may be power-limited when operating in the economy mode. Insome embodiments, the operator may configure the economy mode to presetthe power draw of the various components of temperature control system200. In some embodiments, inputs 302 comprises an input for operating ineconomy mode (e.g., on air conditioning input 306).

Temperature control system 200 may be extended to provide independentcontrol of multiple temperature zones, such as independent temperaturecontrol of cabin 102 and cockpit 104. Each zone may comprise a set ofinputs 302. When providing independent temperature control of multiplezones, each zone may utilize the same compressor 208, condenser HX 210,condenser blower 212, and receiver drier 214. Refrigeration lines mayrun from each zone to connect to the shared compressor 208, condenser HX210, condenser blower 212, and receiver drier 214 as needed. Each zonemay be provided with a separate evaporator HX 216. Additionally, eachzone may share ambient air provided from cabin air static inlet 202.Various other components of temperature control system 200 may beduplicated for each zone. Thus, each zone may comprise a separateelectric heater 218, source selection valve 220, and add-heat valves222. A corresponding supply temperature sensor 226, heat supplytemperature sensor 228, cold supply temperature sensor 230, compartmenttemperature sensor 232, and heater overtemperature switch 236 may beprovided for each temperature zone. In some embodiments, controller 402controls each independent zone. In other embodiments, a separatecontroller 402 is provided for each zone.

While embodiments herein have been described with respect to heating andcooling of an electric aircraft, it should be noted that temperaturecontrol system 200 is not limited to only electric aircraft. Rather,temperature control system 200 may be used on hybrid aircraft andtraditional turbine aircraft as well. Further, temperature controlsystem 200 may be suitably modified to work on pressurized aircraft.

Many different arrangements of the various components depicted, as wellas components not shown, are possible without departing from the spiritand scope of what is claimed herein. Embodiments have been describedwith the intent to be illustrative rather than restrictive. Alternativeembodiments will become apparent to those skilled in the art that do notdepart from what is disclosed. A skilled artisan may develop alternativemeans of implementing the aforementioned improvements without departingfrom what is claimed.

It will be understood that certain features and subcombinations are ofutility and may be employed without reference to other features andsubcombinations and are contemplated within the scope of the claims. Notall steps listed in the various figures need be carried out in thespecific order described.

1. An electric temperature control system for unpressurized aircraft,comprising: an electrical power source for powering the electrictemperature control system; a vapor cycle cooling system for coolingair; an electric heater for heating air; a source selection valve forselecting an air source; at least one air inlet fluidly connected to thesource selection valve; an input device for receiving a user input of atarget temperature value in a compartment of the unpressurized aircraft;a plurality of temperature sensors; and one or more non-transitorycomputer-readable media storing computer-executable instructions that,when executed by at least one processor, carry out actions comprising:receiving, from a temperature sensor of the plurality of temperaturesensors, a compartment temperature value; receiving, from the inputdevice, the target temperature value; determining, based on a differencebetween the compartment temperature value and the target temperaturevalue, whether heating or cooling is required; responsive to determiningthat heating is required, enabling the electric heater; and responsiveto determining that cooling is required, enabling the vapor cyclecooling system.
 2. The electric temperature control system of claim 1,wherein the vapor cycle cooling system comprises: a compressorconfigured to compress a refrigerant; a condenser heat exchangerconfigured to condense the refrigerant; a condenser blower configured toblow air across the condenser heat exchanger; and an evaporator heatexchanger configured to expand the refrigerant, wherein the air isdirected over the evaporator heat exchanger for cooling; and wherein theactions further comprise: modulating a cooling capacity of thecompressor and the condenser blower based on the difference between thecompartment temperature value and the target temperature value.
 3. Theelectric temperature control system of claim 1, wherein the at least oneair inlet comprises an ambient air inlet and a recirculation air inlet,wherein the source selection valve is actuatable between the ambient airinlet or the recirculation air inlet, and wherein the actions furthercomprise: receiving, from an additional temperature sensor of theplurality of temperature sensors, an ambient temperature value; if theambient temperature value is below a maximum cooling value of the vaporcycle cooling system, positioning the source selection valve to receiveair from the ambient air inlet; and if the ambient temperature value isnot below the maximum cooling value of the vapor cycle cooling system,positioning the source selection valve to receive air from therecirculation air inlet.
 4. The electric temperature control system ofclaim 1, wherein the electric heater is a positive temperaturecoefficient heater comprising a plurality of controllable heatingelements, and wherein the actions further comprise: further responsiveto determining that heating is required: setting at least onecontrollable heating element to a full-on state; and modulating anadditional controllable heating element to heat the air near the targettemperature value.
 5. The electric temperature control system of claim1, further comprising: a blower configured to draw air from the at leastone air inlet and direct the air to the compartment; and an additionalinput device for receiving a fan speed setting to control a speed of theblower.
 6. The electric temperature control system of claim 1, furthercomprising: a first valve and a second valve, wherein the first valveand the second valve are configured to direct air to lower outlets ofthe compartment and upper outlets of the compartment.
 7. The electrictemperature control system of claim 6, wherein the actions furthercomprise: responsive to receiving, from the input device, a maximum coldtemperature setting, actuating the first valve and the second valve todirect cooled air to the lower outlets of the compartment.
 8. A methodfor conditioning an unpressurized aircraft using an electric temperaturecontrol system, the method comprising: receiving, from an operator andvia an input device, a target temperature value of a compartment of theunpressurized aircraft; receiving, from a temperature sensor, acompartment temperature value of air in the compartment; determining,based on a difference between the compartment temperature value and thetarget temperature value, whether heating or cooling of the compartmentis required; responsive to determining that cooling is required:enabling a vapor cycle cooling system, the vapor cycle cooling systemcomprising a compressor, a condenser heat exchanger, a condenser blower,and an evaporator heat exchanger; modulating a cooling capacity of thecompressor and the condenser blower based on the difference between thecompartment temperature value and the target temperature value; andcycling refrigerant through the vapor cycle cooling system for coolingof air directed over the evaporator heat exchanger; and responsive todetermining that heating is required: enabling an electric heater;determining an amount of heating to provide to the compartment based onthe difference between the compartment temperature value and the targettemperature value; setting a heating capacity of the electric heaterbased on the difference; and directing, via a blower, the air past theelectric heater for heating and blowing into the compartment.
 9. Themethod of claim 8, further comprising: receiving, from an ambienttemperature sensor, an ambient temperature value; responsive toreceiving the ambient temperature value, selecting an air inlet sourcebased on the ambient temperature value, wherein if the ambienttemperature value is above a threshold temperature value, the air inletsource is selected to be a recirculation air inlet source, wherein ifthe ambient temperature value is below the threshold temperature value,the air inlet source is selected to be an ambient air inlet source, andwherein the threshold temperature value is a maximum cooling temperatureof the vapor cycle cooling system.
 10. The method of claim 8, furthercomprising: receiving, via an additional input device, a fan speedselection; and adjusting a blower speed of the blower based on the fanspeed selection.
 11. The method of claim 10, further comprising:receiving, via the additional input device, a disabling of the blower;and responsive to receiving the disabling of the blower, disabling theelectric temperature control system and positioning an air source valveto provide ambient air to the compartment.
 12. The method of claim 10,further comprising: further responsive to determining that cooling isrequired, directing, via the blower, air from an air inlet source to theevaporator heat exchanger for cooling of the air; and further responsiveto determining that heating is required, directing, via the blower, airfrom the air inlet source to a heat valve for heating of the air by theelectric heater.
 13. The method of claim 8, wherein the method furthercomprises: powering the electric temperature control system with one ofan electric battery pack or an electric generator.
 14. The method ofclaim 8, wherein the method further comprises: responsive to detecting,via a heater over temperature switch, an overheating of the electricheater, disabling the electric heater.
 15. An electric temperaturecontrol system for an unpressurized aircraft, comprising: an electricalpower source for powering the electric temperature control system; avapor cycle cooling system for providing cooling to a compartment of theunpressurized aircraft; an electric heater for providing heating to thecompartment of the unpressurized aircraft; an ambient air inlet fluidlyconnected to a source selection valve; a recirculation air inlet fluidlyconnected to the source selection valve; a blower configured to directair to the vapor cycle cooling system and the electric heater andfurther to the compartment; the source selection valve being actuatableto provide one of ambient air from the ambient air inlet orrecirculation air from the recirculation air inlet to the blower; aninput device for selecting a target temperature value for thecompartment; and at least one controller configured to carry out actionscomprising: determining, based on a difference between the targettemperature value and a compartment temperature value, whether heatingor cooling of the compartment is required; and responsive to determiningwhether heating or cooling of the compartment is required, adjusting aposition of the source selection valve.
 16. The electric temperaturecontrol system of claim 15, wherein the actions further comprise:responsive to determining that heating of the compartment is required:based on the difference between the target temperature value and thecompartment temperature value, determining a target duct temperaturevalue; determining a duct temperature error based on the target ducttemperature value and a measured duct temperature; and determining anumber of heating elements of the electric heater to be turned fully-onand a pulse width modulation duty cycle for an additional heatingelement of the electric heater.
 17. The electric temperature controlsystem of claim 16, wherein the number of heating elements to be turnedfully-on is predetermined based on the duct temperature error.
 18. Theelectric temperature control system of claim 15, wherein theunpressurized aircraft is an electric aircraft substantially lackingbleed air.
 19. The electric temperature control system of claim 15,wherein the actions further comprise: responsive to determining thatcooling of the compartment is required: enabling the vapor cycle coolingsystem; disabling the electric heater; and modulating a cooling capacityof a compressor and a condenser blower of the vapor cycle cooling systembased on the difference between the target temperature value and thecompartment temperature value.
 20. The electric temperature controlsystem of claim 19, wherein the actions further comprise: responsive toreceiving a maximum cooling input from the input device, setting thecooling capacity of the compressor to a maximum cooling capacity.